Hypothesis: Risk for the introduction and establishment of exotic arboviruses can be delineated by landscape features and the abundance and vector competence of the endemic mosquito fauna. Skill in forecasting risk for the introduction of new viruses in time and space can be assessed retrospectively by assessing factors facilitating the transmission of endemic encephalitis viruses and the current invasion of West Nile virus. Our overall goal is to provide health planners, emergency services and veterinary personnel with a decision support system that assesses the potential of the California landscape to support mosquito transmission of introduced arboviruses, including Japanese encephalitis, Ross River, and Rift Valley Fever.